This invention relates to methods of bearing design, manufacture and assembly and specifically to a double row ball bearing of the type in which a separable inner race is integrally retained to a central spindle with an improved method of maintaining the shape and position of the inner race during the bearing retention feature formation process.
Wheel bearing assemblies typically embody a dual row of rolling elements with varying degrees of raceway integration into the supporting structural members. These assemblies typically incorporate a rotating inner member or spindle that provides a wheel attachment feature and an integral bearing race member. It also typically incorporates a non-rotating outer member or hub that provides attachment to the vehicle and may have both bearing members integrated into the structural member. The design permits relative rotation between the spindle and hub. For wheel bearing assemblies that do not have both race ways integrated with the spindle, the inboard separable inner race member must be secured to the spindle. The inner race is typically secured rotationally to the spindle member via an interference fit. Some applications are such that additional retention features are required to maintain the axial position of the inner race relative to the outer race in order to maintain bearing preload and to maintain wheel and bearing assembly integrity. This has been accomplished in several ways that have presented unique problems. One primary method, used preferably due to its lower cost than other methods, is to plastically deform the end of the spindle along its axis to form a radially extending tab of spindle material to permanently axially retain the separable bearing member on the spindle. One difficulty with this method is that in plastically deforming the spindle the bearing member is overstressed due to excessive radial expansion. This stress can lead to premature failure of the bearing assembly caused by noise associated with fracturing of the inner member, relative rotation between the bearing member and the spindle, noise associated with reduced rolling contact fatigue life of the inner member, and the like.
Many ways of attempting to reduce the stress on the bearing member during this process have been used. However, most of these methods also have complications of either not sufficiently reducing the stress or are significantly complex and/or costly. One method includes trying to accurately predict the forces involved in deforming the spindle such that the process can be controlled to minimize the stress on the bearing member. Unfortunately, this technique has not proven successful in reducing forming related stresses sufficiently to avoid premature failure of the bearing member. Another technique includes adding material to the bearing member to compensate for the deformation caused by the stresses. While the extra material does increase the strength of the bearing member, the changed geometry affects the design of the entire assembly often resulting in unacceptable space requirements for the assembly.
Other methods involve incorporating design features into the inner member or spindle to allow for expansion of the spindle during forming. Such features as reduced initial press-fit and spindle swelling xe2x80x9creliefxe2x80x9d designs have proven inconsistently effective in preventing excessive hoop stress development in the inner race member. One such design is described in U.S. Pat. No. 5,822,859. In this reference the inner race member contains a shallow conical relieved surface along an inner edge of the race member allowing expansion of the member during forming. Another method involves alternative methods of deforming the spindle including heat rather than mechanical force. Again the use of such a process as heat significantly increases the complexity and cost of forming the bearing assembly.
Therefore, an apparatus and method for securing the inner race to the bearing assembly is needed such that the inner member is not significantly disturbed during the retention forming process thereby not affecting the lifespan of the assembly.
The present invention provides a wheel bearing assembly for supporting a wheel. The assembly includes a spindle defining a rotational axis with a flange for securing the wheel thereto and a hub for attaching the assembly to a vehicle. The assembly includes an inner rack bearing member held in place by the spindle spaced from the hub by a plurality of rolling elements interposed between the inner bearing member and the hub to permit relative rotation between the hub and the spindle about the rotational axis. An outer surface of the inner bearing member has a featured surface. A force is applied to the feature on the outer surface of the inner bearing member by a mating feature on a tool during the forming of an end of the spindle. The mating feature of the tool and the inner race bearing member create a radial force that opposes the forces on the inner race bearing member imposed during the spindle forming process thereby reducing the radial expansion stress imposed on the inner bearing member. A constraining of the inner race member during the formation of the spindle also helps prevent a rotation between the inner race member and the spindle during use that may occur if the inner race is allowed to expand during forming of the spindle as in the prior art.
Another aspect of the present invention provides a method of securing a separable inner race to a spindle whereby the inner race is not overstressed during the process. First, a bearing member (separable race) is provided having a featured outer surface. The spindle or wheel assembly member has an interior cavity defined by an interior surface. Second, the bearing member is arranged onto the wheel assembly member. Next, a forming tool is inserted into the interior cavity of the wheel assembly member and a process tool with a featured outer surface is mated with the outer surface of the bearing member. An axial and resultant tangential force is applied against the bearing member by the process tool to reduce the stresses against the inner race introduced during the deforming of the spindle around the bearing member by the forming tool.
Accordingly, an apparatus and method is introduced for securing an inner race to a wheel assembly in which the resulting stresses to the inner bearing assembly are minimized during, the process thereby maintaining the bearing assembly quality and performance.